1. Field of the Invention
The present invention relates to a thin film transistor substrate and a method of manufacturing the same. More particularly, the present invention relates to a thin film transistor substrate with good process efficiency and a method of manufacturing the same.
2. Description of the Related Art
Recently, in liquid crystal displays (LCDs) used as display devices for notebook computers or other portable devices, driving methods thereof are shifting from a simple matrix type to an active matrix type. In particular, a thin-film transistor (TFT) active matrix driving method in which a plurality TFTs are formed on a glass substrate has become the mainstream technology for driving the LCDs.
A TFT generally includes a gate electrode as a part of a gate line, a semiconductor layer forming a channel, a source electrode as a part of a data line, and a drain electrode opposite the source electrode about the semiconductor layer. The TFT is generally used as a switching element for transmitting to or blocking from a pixel electrode a picture signal received through the data line by a scanning signal transferred through the gate line.
The semiconductor layer typically comprises amorphous silicon or polycrystalline silicon. Thin-film transistors are categorized into a bottom-gate type and a top-gate type according to the relative position of the semiconductor layer to a gate electrode. A polycrystalline silicon TFT is usually of a top gate type in which a gate electrode is formed above a semiconductor layer.
Along with the development of various crystallization techniques using lasers, such a polycrystalline silicon TFT can be manufactured in a temperature range similar to that of an amorphous silicon TFT while having higher electron or hole mobility than the amorphous silicon TFT, thereby realizing a Complementary Metal-Oxide Semiconductor (CMOS) TFT including an NMOS TFT with an n channel and a PMOS TFT with a p channel. Consequently, the polycrystalline silicon TFT can be utilized primarily for a driving circuit on a large-area glass substrate.
In conventional methods of manufacturing CMOS thin film transistors, however, the upper structures of semiconductor layers and ion implantation regions in the semiconductor layers of NMOS and PMOS transistors are formed using separate photolithography processes, which makes a manufacturing process complicated and increases manufacturing costs.